This invention relates generally to semiconductor processing utilizing a plasma, and specifically relates to the improvement of plasma distribution and process performance within a plasma generated and sustained through inductive coupling.
Gas plasma generation is widely used in a variety of integrated circuit (IC) fabrication processes, including plasma etching, plasma enhanced chemical vapor deposition (PECVD), and plasma sputter deposition applications. Generally, plasmas are produced within a process chamber by introducing a low-pressure process gas into the chamber and then directing electrical energy into the chamber for creating an electrical field therein. The electrical field creates an electron flow within the chamber which ionizes individual gas atoms and molecules by transferring kinetic energy through individual electron-gas molecule collisions. The electrons are accelerated within the electric field, producing efficient ionization. The ionized particles of the gas and free electrons collectively form what is referred to as a gas plasma or discharge. The plasma may exist at various ionization levels from 10xe2x88x926 up to fully ionized plasma (based on the fraction of ionized particles with respect to the total number of particles).
The plasma particles will generally be positively charged, and are commonly utilized for etching a surface of a substrate within the chamber or depositing a layer of material onto such a substrate. Within an etching process, the substrate may be negatively biased such that the positive plasma particles are attracted to the substrate surface to bombard the surface and thus remove surface particles or etch the substrate. In a sputter deposition process, a target may be positioned within the chamber opposite the substrate. The target is then biased so that plasma particles bombard the target and dislodge, or xe2x80x9csputter,xe2x80x9d target particles therefrom. The sputtered target particles then deposit upon the substrate to form a material layer on an exposed surface thereof. In a plasma enhanced CVD process, the electrically neutral, active, radicals form a deposited layer on exposed surfaces.
Generally, there are various different ways of producing a plasma within a process chamber. For example, a pair of opposing electrodes might be oriented within the chamber to capacitatively couple energy to the plasma. A microwave resonant chamber utilizing ultra-high frequency microwave fields might also be utilized. Electron cyclotron resonance (ECR) devices, on the other hand, use controlled magnetic fields in conjunction with microwave energy to induce circular electron flow within a process gas to create and sustain a plasma. Inductive coupling processes are also popular, and are particularly desirable for their capability of producing a high-density plasma. Inductively coupled plasmas (ICP) generally utilize a shaped coil or antenna positioned with respect to the processing chamber to inductively couple energy into the processing chamber and thus create and sustain a plasma therein.
For example, in one particular design for an inductively coupled plasma (ICP) system, an inductive coil or antenna is positioned proximate the top portion of the chamber to create a plasma within the chamber. More specifically, the antenna is positioned on one side of a dielectric plate or window at the top of the processing chamber, and electrical energy from the antenna is coupled through the dielectric window and into the plasma. One such design is illustrated in U.S. Pat. No. 5,556,521 which is commonly owned with the present application.
In an alternative ICP processing system, a helical or solenoidal-shaped coil is wound around the outside of a sidewall portion of the processing chamber to inductively couple energy to the plasma through the chamber sidewall, rather than through the top of the chamber. In such a system, a portion of the chamber sidewall is fabricated from a dielectric material through which the inductively coupled energy may pass. One suitable dielectric material for a window or chamber sidewall is quartz. Various ICP systems are known and utilized in the art, as evidenced by various issued patents directed to particular ICP details, such as plasma uniformity, RF matching, and the performance characteristics of the antennas or other inductive elements.
The geometry of an ICP system is a significant factor in determining both the plasma density and uniformity, and ultimately, the processing uniformity over the area of the substrate. For today""s processes, it is desirable to produce a uniform, high-density plasma, over a significantly large area so that large substrate sizes might be accommodated. For example, manufacturing of today""s ultra large-scale integrated (ULSI) circuits requires a dense, uniform plasma over large substrates having diameters of approximately 200 mm.
More specifically, in an ICP system, the plasma is excited by heating or exciting electrons in the plasma region of the processing chamber. The inductive currents which heat the plasma electrons are derived from oscillating magnetic fields which are produced proximate the inside of the dielectric window or sidewall by RF currents within the inductive antenna or coil. The spatial distribution of those magnetic fields is a function of the sum of the individual magnetic fields produced by each portion or segment of the antenna or coil conductor. Therefore, the geometry of the inductive antenna or coil significantly determines the spatial distribution of the plasma, and particularly the spatial distribution and uniformity of the plasma ion density within the process chamber. As one example, an antenna having an xe2x80x98Sxe2x80x99 shape, such as that disclosed in U.S. Pat. No. 5,669,975, establishes a significant ion density in the central area of the antenna. At higher RF power levels, the outer portions of the antenna will also contribute significantly to plasma ionization. While a significant advantage of an ICP system utilizing such an antenna is the linearity of the system with respect to the power delivered to the antenna and also the radius of the process chamber, and while the current ICP systems and antenna designs utilized therein have provided sufficient plasma generation, such systems still have certain drawbacks.
For example, within the confines of existing ICP systems and antenna configurations, it is difficult to scale the process chamber to a larger size for handling larger substrates without significantly increasing the dimensions of the antenna or coil. An ICP antenna with a larger footprint must be accommodated with expensive modification to the processing system. Furthermore, larger antennas and their associated plasmas exhibit greater sensitivity to process parameters within the chamber. For example, the plasma process, such as an etch or deposition process, becomes more sensitive to process parameters such as the substrate-to-target distance within a sputtering system, the target material within a sputtering system, the pressure within the process chamber, and the height and width configuration of the chamber.
Furthermore, current ICP systems utilizing planar spiral antennas have exhibited asymmetry wherein the distribution of the plasma is not aligned with the central axis of the chamber. Such plasma asymmetry degrades the uniformity of the plasma and the uniformity of the deposition or etch process, thereby affecting the overall system efficiency. Still further, planar antennas may exhibit a ring or doughnut-shaped plasma for one process and corresponding set of parameters, while creating a centrally peaked plasma for another process and other parameters. Accordingly, the plasma shape and uniformity is not consistent within such ICP systems and will be process dependent. Therefore, the overall IC fabrication process will not be consistent from one plasma process to another plasma process.
Another drawback with planar antenna systems utilizing an S-shaped antenna or coil, is that the outer portions of the coil marginally affect the plasmas created by the central region of the coil, thus giving an azimuthal dependence within the plasma, and a corresponding azimuthal dependence in the etched or deposited films on the substrate. That is, along one axis of the plane defined by the coil, the plasma will have a different uniformity and density than along another planar axis of the coil.
Various ICP antenna designs have been utilized for plasma processing, as evidenced by the above-mentioned and other U.S. patents directed to plasma processing systems.
Patent application, Ser. No. 09/277,526, entitled xe2x80x9cProcess, Apparatus, and Method for Improving Plasma Distribution and Performance in an Inductively Coupled Plasma,xe2x80x9d and filed on Mar. 26, 1999, discloses a system utilizing an antenna design which addresses various of the drawbacks of the prior art, and is incorporated herein by reference in its entirety. It is an objective to further modify and improve on antenna designs as disclosed in that application.
It is another objective of the present invention to overcome drawbacks in the prior art and provide a plasma processing system, and particularly an ICP system, in which a dense, uniform plasma is created.
It is another objective of the present invention to provide a uniform plasma which is less dependent upon the size and shape of the process chamber than current plasma processing systems.
It is still another objective to provide a plasma which is symmetrical in the processing chamber.
It is another objective of the present invention to provide a uniform, dense plasma over a large area, such as an area sufficient to handle a 200 mm wafer, while maintaining a compact and inexpensive design of the inductive coil or antenna.
It is still another objective of the present invention to provide consistent plasma generation and thereby provide consistent processes, such as etch processes and deposition processes, which are less dependent upon process parameters, such as pressure and/or chamber geometry or size.
These and other objectives will become more readily apparent from the description of the invention set forth below.
The above objectives of the present invention are addressed by a processing system for processing a substrate with a plasma which utilizes uniquely shaped inductive elements for generating and maintaining the plasma. The systems described herein utilizing an inductive element configured in accordance with the principles of the present invention create a uniform and dense plasma over a significantly large area in the chamber without requiring a significant increase in chamber size for accommodating the inductive element. Whereas, in prior art plasma processing systems, increased energy introduced into the plasma required a significant increase in the size of the inductive element as well as the corresponding size of the processing chamber, the present invention provides dense uniform plasmas while maintaining a compact, and therefore relatively inexpensive processing system.
Specifically, the processing system comprises a processing chamber defining a processing space therein, and including a substrate support for supporting a substrate within the processing space. A gas inlet introduces a process gas into the processing space, and a plasma source of the system is operable for creating a plasma from the process gas. The plasma source comprises a dielectric window having a generally planar surface, which interfaces with the processing chamber proximate the processing space where the plasma is to be created. An inductive element, or antenna element, is positioned outside of the chamber and proximate the dielectric window and is operable for coupling electrical energy inductively through the dielectric window and into the processing space to create and maintain a plasma therein.
The invention contemplates various different designs of the antenna or inductive element for achieving the goals of the present invention. In one embodiment, the antenna is formed with opposing ends to which a power supply is coupled for inductively coupling electrical energy into the processing space. The antenna element comprises an electrical conductor which is configured to have multiple turns which are wound successively along the length of the antenna element between the opposing ends. Portions or segments of the conductor turns extend transversely with respect to the opposing ends of the antenna element and are oriented in a plane which is generally parallel to the planar surface of the dielectric window. In one embodiment, the transverse turn portions curve concavely with respect to the respective ends of the antenna. In another embodiment, they curve convexly with respect to the antenna ends. More specifically, the antenna element may be considered to have two cooperating halves positioned on either side of a midline. Thus, the opposing ends of the antenna element are on either side of the midline. Transverse turn portions of one half curve concavely with respect to the respective antenna element end of that one half, while portions of the other half similarly curve concavely, but with respect to the other antenna element end.
In another embodiment of the invention, the inductive element comprises a coil which has multiple coil turns disposed successively along the length of the coil and from one side of the dielectric window. At least one of the coil turns is oriented in a first plane, and another of the coil turns is oriented in a second plane which is angled from the first plane. Specifically, multiple coil turns are oriented within the first plane and multiple coil turns are also oriented in planes which are angled from the first plane. The first plane is oriented generally parallel to a planar surface of the dielectric window. In that way, the coil turns within the first plane lie flat against the dielectric window. The coil turns angled from the first plane are disposed at an angle to the dielectric window. In one embodiment, the coil turns which are angled with respect to the first plane are oriented to be generally perpendicular to the first plane. In other embodiments, the coil turns are angled at less than 90xc2x0 from the first plane. Preferably, multiple sets of coil turns are oriented in the first plane whereas the coil turns that are angled from the first plane are positioned between those sets of coil turns. In that way, a uniform plasma is created. By maintaining some coil turns of the inductive element within a plane that is flat against the dielectric window, plasma stability is maintained. Utilizing coil turns which are angled from the planar dielectric window provides for a greater number of coil turns along the dielectric window than would be achieved utilizing a generally planar coil of generally the same dimensions. That is, the inventive element creates a dense uniform plasma utilizing a compact design which does not require significant increases in the size of the processing chamber. The coil turns oriented within the first plane are coplanar and concentric, and define an inner coil end and an outer coil end. In alternative embodiments of the invention, the coil turns which are angled with respect to the planar dielectric window are coupled to the coil turns within the first plane, either at the inner coil end or at the outer coil end to vary the configuration of the inductive element and thus vary its effect on the plasma.
In accordance with another aspect of the present invention, the processing system may comprise a second inductive element, such as a helical coil wrapped around a chamber sidewall section which is utilized in conjunction with the inventive inductive element. In that way, electrical energy is inductively introduced into a plasma both from the end of the chamber as well as from the sidewall of the chamber. Preferably, each of the inductive elements is coupled to an independent electrical energy source for independently biasing the first and second inductive elements. Also, Faraday shields are preferably positioned between each of the inductive elements and plasma to enhance the inductive coupling of electrical energy into the plasma and reduce capacitive coupling.
The present invention, utilizing multiple, independently-biased inductive elements may be utilized for a variety of different processes, including etching processes and deposition processes. The present invention has been found to be particularly useful for ionized physical vapor deposition (iPVD). To that end, the target material might be positioned proximate the dielectric window to be sputtered by a plasma generated by the inventive inductive element proximate that dielectric window.
In accordance with another aspect of the present invention, the inductive element utilized with the dielectric window at an end wall of the chamber comprises a coil having multiple coil turns. However, rather than the coil turns being within a plane which is parallel to the planar dielectric window and other planes which are angled from the planar dielectric window, the alternative inductive element has portions of the various coil turns which are oriented and spaced in generally horizontal planes to form vertically stacked coil turns. The vertically stacked coil turns are oriented generally parallel to the dielectric window. Again, utilizing stacked coil turns, a greater number of coil turns may be utilized within the inductive element without increasing the overall horizontal footprint of the element and thus increasing the size of the processing chamber that is necessary for accommodating the inductive element.
In accordance with another aspect of the present invention, the inductive element is not in the form of a coil, but rather, comprises a plurality of repeated conductor segments arranged in a non-coil fashion and positioned in a circular pattern around the center of the inductive element. In one embodiment, the repeated conductor segments of the inductive element are disposed to extend radially outwardly from the center of the inductive element. In another embodiment, the repeated segments themselves form individual coils. The coils are arranged in a circular pattern around the center of the inductive element and are not simply successive individual turns of a larger coil element. The inductive element comprising a plurality of repeated conductor segments may be formed as repeated segments within a single plane, or may comprise layers of repeated conductor segments. For example, the repeated conductor segments of the inductive element may form a first layer, and a second layer may be formed by similar repeated conductor segments which are generally co-extensive with those segments in the first layer. The repeated conductor segments might also be utilized to couple energy into the chamber from both an end wall portion of the chamber and a sidewall portion. To that end, the repeated conductor segments include horizontal segments oriented along a chamber end wall and vertical segments oriented along a sidewall.
In accordance with another aspect of the present invention, a processing system may utilize an inductive element which is operable for coupling energy to the processing space simultaneously from both a sidewall portion and an end wall portion of the chamber. To that end, the processing chamber has a sidewall portion and end wall portion which are formed of a dielectric material. In conventional processing chambers, an end wall portion, such as a dielectric window, might be utilized in conjunctive with a planar conductive element. Alternatively, a conventional processing chamber might utilize a sidewall formed of a dielectric material wherein a helical coil is wrapped around a sidewall for inductively coupling energy into the system. In accordance with the principles of the present invention, the processing chamber includes both a sidewall portion and an end wall portion formed of a dielectric material. The inductive element comprises a segment thereof which is oriented along the chamber sidewall portion and also a segment thereof which is oriented along the chamber end wall portion for coupling energy simultaneously into the processing space, both through the sidewall and end wall portions of the chamber. To that end, the inductive element comprises a coil having multiple coil turns. Segments of the coil turns are oriented along the chamber sidewall portion, and other segments of the coil turns are oriented along the chamber end wall portion. The coil may be configured such that sections of the coil turn segments which are oriented along the sidewall are angled from each other. For example, sidewall sections of the coil turns might be oriented generally perpendicularly to other sidewall sections of the coil turns. Alternatively, the sidewall sections might be disposed at various different angles rather than a right angle associated with a perpendicular orientation. The coil generally has sets of coil turns with one set of turns being positioned generally along one side of the chamber and another set of turns being positioned generally along another side of the chamber.
The processing system of the present invention utilizing the inventive inductive elements provide dense, uniform plasmas in a compact design. The inventive primary inductive elements may be utilized in conjunction with secondary inductive elements for further enhancing plasma processes, such as ionized physical vapor deposition. The invention may be utilized to induce greater amounts of electrical energy into a sustained plasma without requiring an expensive increase in the size of the chamber necessary for accommodating the inductive element. These advantages and other advantages of the present invention are set forth in the detailed description hereinbelow.